Robinmask’s mask...

Excuse me if the answer is simple, or explained in the story (I’ve only managed to watch about 6 episodes of the kinnikuman anime and none of the manga) but what is the significance of the damage on Robinmask’s mask? The gouge onthe forehead section?

Well in fact it does get repaired, In Nisei after Kevin modified the mask to look like his, in the Chojin Olympics: The Resurrection final, after Kevin won, the mask seemed to heal. signifying that the blood feud with The Kinniku clan was over.